In the first phase of this project, it was shown that by utilizing innovative technologies it was possible to allow below the knee amputees to walk and run using a single powered prosthetic device. In the second phase of this project, it will be shown that the key technological advancements and optimizations will allow the a single powered device to perform walking, running, and transitioning between the two while on level ground and slopes, as well as being rugged and user friendly enough that it can be worn during every day activities. Current users of passive prosthetic devices typically expend more energy; have reduced ankle motion and power; and increased gait asymmetry resulting in joint and back pain. Augmenting ankle power with a robotic tendon actuator will restore near able bodied function improving quality of life. The current state of the art powered prosthetic devices have limited battery life, are relatively loud, have a slow top running speed, and are not rugged. During this project, key technologies being developed by SpringActive will be used to lower electrical current requirements, decrease actuator acceleration, increase battery life, reduce noise, and increase the top running speed. Testing of the PWR ankle will be performed by the Minneapolis VA Health Care System with technical device support from SpringActive. We hypothesize that the PWR ankle will produce net positive work during fast walking, produce changes in effective alignment of the ankle for walking on different sloped surfaces, indicating adaptation to the slopes, and improve limb loading symmetry compared with use of passive prostheses.